Process for preventing the polymerization of conjugated dienes

ABSTRACT

A process for preventing the polymerization of conjugated dienes in solvents at high temperatures comprising the addition of at least one compound selected from the group consisting of organic phosphoric acid esters of the specific general formula, pyridine, nuclear substituted derivatives of pyridine wherein the substituents are alkyl groups, quinoline, nuclear substituted derivatives of quinoline wherein the substituents are alkyl groups, and anthracene, to the solvent containing a conjugated diene as inhibitor.

[451 Mar. 26,1974

PROCESS FOR PREVENTING THE POLYMERIZATION OF CONJUGATED DIENES Inventors: Tatsusuke Chikatsu; Yoshinori Yoshida; Shinichi Shimokawa; Toshio Akimoto, all of Yokkaichi,

Japan [73] Assignee: Japan Synthetic Rubber Company Limited, Tokyo, Japan [22] Filed: Mar. 9, 1971 [21] Appl. No.: 122,514

[52] US. Cl... 260/6815 R, 260/6665, 208/48 AA, 203/65, 203/9 [51] Int. Cl. C07c 7/00, C07c 7/18 [58] Field of Search 260/6665, 681.5; 208/48, 208/48 AA; 203/65, 9

[56] References Cited UNITED STATES PATENTS 3,565,855 2/1971 Meltsner 260/4585 3,567,682 3/1971 Zaweski et al 260/4585 3,558,470 l/1926 Gillespie et al. 203/48 3,265,751 8/1966 McCoy et al. 260/6665 3,047,503 7/1962 Jaffe' et al. 252/52 2,613,175 10/1952 Johnstone et al. 202/57 3,448,015 6/1969 Rogers 203/8 3,215,720 11/1965 Atwood et al. 260/461 3,340,160 9/1967 Waldby 203/9 Primary ExaminerDelbert E. Gantz Assistant Examiner-Juanita M. Nelson Attorney, Agent, or Firm-Toren and McGeady [5 7] ABSTRACT A process for preventing the polymerization of conjugated dienes in solvents at high temperatures comprising the addition of at least one compound selected from the group consisting of organic phosphoric acid esters of the specific general formula, pyridine, nuclear substituted derivatives of pyridine wherein the substituents are alkyl groups, quinoline, nuclear substituted derivatives of quinoline wherein the substituents are alkyl groups, and anthracene, to the solvent containing a conjugated diene as inhibitor.

11 Claims, No Drawings PROCESS FOR PREVENTING THE POLYMERIZATION OF CONJUGATED DIENES This invention relates to a process for preventing the polymerization of conjugated dienes and, more particularly, to a process for preventing the polymerization of conjugated dienes in organic solvents at relatively high temperature.

Processes for extractive distillation or absorption by solvent have been known for the separation and refining in high yield of high purity butadiene or isoprene, both industrially valuable materials, respectively from the C,, hydrocarbon fraction of naphtha cracked oil which contains butadiene, butane, butylene and isobutylene as main components or from the C hydrocarbon fraction which contains pentane, pentene, isoprene and piperylene as main components.

It is also known that for those processes solvents, such as acetonitrile (ACN), N-methyl pyrrolidone (NMP), dimethyl formamide (DMF), dimethyl acetamide (DMAC) and furfural, are used.

Usually the conjugated dienes above referred to are known to be readily oxidized at normal temperature by oxygen and the like present in the solutions and tend to produce polymers when allowed to stand for long. In the operation for separation and refining by a conventional extractive distillation or absorption-process, solvents containing butadiene or isoprene are inevitably subjected to temperatures above the boiling point of the C or C hydrocarbon fractions, e.g., over 70 C. As a consequence, the polymerization of butadiene or isoprene in the solvent is accelerated and the polymerization product is deposited. This phenomenon is easily observed because the originally transparent solution is colored with time until it is opaque and a deposition of polymer occurs.

Such a polymer deposit causes various troubles. For example, it forms a thin polymer film over the inner walls of the equipment, clogs the passages-and reduces the extraction efficiency, thus making it practically difficult to operate the equipment continuously for many hours.

It is an object of the present invention to overcome the foregoing difficulties, that is, to prevent the polymerization of the conjugated dienes during the operation above described.

To achieve this object diversified studies have been made, and it has now been found that the polymerization of conjugated dienes can be effectively prevented by adding an organic phosphoric acid ester which may be represented as pyridine, quinoline, anthracene, a compound having an alkyl group in the nuclear substituent of pyridine, a compound having an alkyl group in the nuclear substituent of quinoline, etc. to a solvent, such as ACN, NMP, DMF or DMAC, for the extraction of a conjugated diene.

Thus, the present invention provides a process for preventing the polymerization of conjugated dienes in solvents at high temperature characterized by the addition of at least one compound selected from the class consisting of organic phosphoric acid esters of the general formula v(wherein R,, R and R are phenyl or nuclear substituted phenyl groups, the substituents being alkyl groups, phenyl group or halogen atoms, alkyl or halogenated alkyl groups or allyl group), pyridine, nuclear substituted derivatives of pyridine wherein the substituents are alkyl groups, quinoline, nuclear substituted derivatives of quinoline wherein the substituents are alkyl groups, and anthracene, to a solvent containing a conjugated diene. 1

Among the organic phosphoric acid esters which may be advantageously used for the invention are such compounds as triphenyl phosphate and-nuclear substituted derivatives thereof wherein the substituents are alkyl groups, phenyl groups or halogen atoms, trialkyl phosphates with or without substitution of the hydrogen of the alkyl group by halogen atom, allylbiphenyl phosphate, diallylphenyl phosphate and other phenyl groupand allyl groupcontaining compounds.

Suitable triphenyl phosphate and nuclear substituted products thereof are triphenyl phosphate, tri(o-cresyl) phosphate, tri(m-cresyl)'phosphate, tri(p-cresyl) phos phate, trixylenyl phosphate, tris(4-t-butylphenyl) phosphate, tris(o-biphenylyl) phosphate, etc. wherein the substituents are alkyl groups, phenyl groups or halogen atoms.

Suitable trialkyl phosphates and halogen substituted derivatives thereof are trimethyl phosphate, triethyl phosphate, tri-n-propyl phosphate, tri-iso-propyl phosphate, tri-n-butyl phosphate, tri-sec-butyl phosphate, tri-n-amyl phosphate, trihexyl phosphate, triheptyl phosphate, trioctyl phosphate and other organic phosphoric acid esters wherein the alkyl groups have from 1 to 8 carbon atoms; and tri(Z-chloroethyl) phosphate, tri(2-bromoethyl) phosphate, tri(3-chloropropyl) phosphate, tri(3-bromopropyl) phosphate, tri(3- iodopropyl) phosphate, tri(2,3-dichloropropyl) phosphate, tri(2,3-dibromopropyl) phosphate, tri(2,3- diiodopropyl) phosphate, tri(4-chlorobutyl) phosphate, tri(4-bromobutyl) phosphate, tri(4-iodobutyl) phosphate and other organic phosphoric acid esters containing halogen atom-substituted alkyl groups. As the organic phosphoric acid esters which contain phenyl and allyl groups, diallylphenyl phosphate and allylbiphenyl phosphate are desirable.

Examples of the compounds having alkyl groups in the nuclear substituents of pyridine are: picolines, such as Z-methyl-pyridine, 3-methyl-pyridine and 4-methylpyridine; lutidines, such as 2,3-dimethyl pyridine, 2,4- dimethyl pyridine, 2-ethyl pyridine and S-ethyl pyridine; collidines, such as 2-methyl-4-ethyl pyridine, 2-

methyl-S-ethyl pyridine, 2-propyl pyridine, 2-isopropyl pyridine and 2,4,5-trimethyl pyridine; and parvolines, such as 2,3,4,5-tetramethyl pyridine and 2-butyl pyridine. Examples of compounds having alkyl groups substituted in the nuclear of quinoline are alkyl quinolines, such as 2-methyl quinoline, 3-methyl quinoline, 2,3- dimethyl quinoline, 3,4-dimethyl quinoline, 2-ethyl quinoline and 4-ethyl quinoline.

These polymerization inhibitors are capable of either preventing the polymerization of conjugated dienes at high temperature or permitting the chain transfer of polymerization thereby to avoid the production of any solvent-insoluble polymer. The above-mentioned organic phosphoric acid esters have particularly good polymerization-inhibiting. effect.

Those polymerization inhibitors prove fairly effective when used singly. However, the effect of'preventing the polymerization of conjugated dienes which is achieved by the addition of those compounds according to the present invention is much enhanced when the compounds are used in combination with an extensive variety of substances, e.g., sodium nitrite, potassium nitrite, sodium sulfide, phenolic compounds and aromatic amine compounds, which are usually employed as polymerization inhibitors or antioxidants for unsaturated compounds. This is because the polymerization inhibitors may be classified from the viewpoint of their mechanisms as such, into two types, i.e., radical chain reaction inhibitors and peroxide decomposing agents, and it is considered that the polymer production is based on the two stages of radical initiation and radical growth. Thus, the process of the invention makes it possible to promote the effect of preventing the polymerization of a conjugated diene in a solvent at elevated temperature remarkably by taking advantage of the synergistic action of the two substances which possess different polymerization inhibiting abilities. The combined use of the different inhibitors proves most beneficial for the prevention of polymerization of isoprene, especially.

The known polymerization inhibitors or antioxidants for unsaturated compounds used in combination with the inhibitors of the present invention include: I

l. NaNO KNO Na S, methylene blue and mercaptobenzothiazole;

2. Phenolic compounds, e.g., hydroquinones, such as 2,5-di-tert.-butyl hydroquinone and 2,5-di-tert.- amyl hydroquinone; phenols, such as ophenylphenol, 2,6-di-tert.-buty1-p-phenylphenol, butylated hydroxytoluene and p-methoxyphenol; cresols, such as 2,6-di-tert.-butyl-p-cresol; catechols, such as di-tert.-butyl catechol and p-tert.- butyl catechol; bisphenols, such as 2,2-methylene-- bis(4-methyl-6-tert.-butylphenol) and 4,4- methylene-bis(2,6-di-tert.-butylphenol; naphthols, such as a-naphthol, B-naphthol, 1,1 '-methylenebis-2-naphthol; and aminophenols, such as paminophenol and 2,6-di-tert.-butyl-a-dimethyleneamine-p-cresol; and

3. Aromatic amine compounds, e.g., p,pdiaminodiphenylmethane, N-phenylanaphthylamine, N-phenyl-Bnaphthylamine, p-isopropoxydiphenylamine, 4,4'-dimethoxydiphenylamine, N,N'-dipheny-p-phenylenediamine, N,N- diphenylethylene diamine, N,N-di-otolylethylenediamine, N,N'-di-B-Naphthyl-pphenylene diamine, octyldiphenylamines (monoand di-), and 2,4-diaminotoluene.

In accordance with the present invention, the effect of preventing the polymerization of butadiene and isoprene is adequately achieved even in the presence of iron rust which is generally believed contributory to cause the polymerization of dienes. This eliminates the use of expensive special steel as material of the equipment and makes possible steady, continuous operation for an extended period of time. I

The amounts of the polymerization inhibitors to be added are varied according to the type and water content of the solvent and the operating conditions to be employed. Usually, however, the purpose is achieved by adding the first inhibitors, i.e., organic phosphoric acid esters, pyridine, quinoline, anthracene, the nuclear substituted derivatives of pyridine and quinoline, etc., in an amount of 0.01 to 10 percent, preferably 0.05 to 5 percent, by weight on the basis of the solvent, and adding the second inhibitors, i.e., sodium nitrite, phenolic compounds, aromatic amine compounds, etc., in an amount of 0.001 to 5 percent, preferably 0.005 to 1 percent, by weight on the basis of the solvent.

The said inhibitors classified into the two groups as above may be added singly or in combination, respectively, to attain the desired effect.

Of course, the amounts of these addition agents are not confined within the limits above specified.

The present invention is illustrated by the following examples.

Example 1 parts of dimethyl formamide containing 5 percent by weight of water and 30 parts of butadiene were mixed and, after the addition of the following inhibitors, the mixtures were treated with heat for 70 hours in the presence of iron rust at a temperature of 150 C and at a gauge pressure maintained at 5.0 kglcm and then the conditions of the products were investigated. Compositions free from water were treated under the same conditions. The results are shown in Table 1.

Example 2 Under the same conditions as described in Example 1 except that acetoni trile was used as the solvent, test solutions were prepared. With various inhibitors as given in Table 2, the preparations were treated with heat for 70 hours in the presence of iron rust at 120 C. The results were shown in Table 2.

Table l Polymerization inhibitor Condition Polymer No. lst inhibitors (wt.%) 2nd inhibitors (ppm) after heat content treatment (WL7r) 1 None None Polymer deposits 2 do. Sodium Slightly 2.2

nitrite whitens Table l- Continued Polymerization inhibitor Condition Polymer No 1st inhibitors (wt.%) 2nd inhibitors (ppm) after heat content treatment (wt.%)

3 Triphenyl 0.5 None do. 1.7

phosphate 4 do 0.5 Sodium 100 Clear 03 nitrite 5 Triphcnyl 0.5 Potassium 100 Clear 0.5

phosphate nitrite 6 do. 0.5 Sodium 100 do. 0.8

sulfide 7 do. 0.5 p-t-Butyl 100 do. 1.0

catechol 8 do. 1.0 Phenyl-/3- 100 do. 1.2

naphthylamine 9 Tricresyl 1.0 None do. 0.5

a phosphate 10 do. 0.5 Sodium 100 do. 0.4

nitrite l 1 Di-n-butyl 0.5 do. 100 do. 0.7

phosphate 12 Tri(n)buty1 1.0 None do. 0.8

phosphate 13 Tris(4-t- 0.5 Sodium 100 do. 0.3

butylphenyl nitrite phosphate) 14 Tris(o- 0.5 do. 100 do. 1.0

biphenylyl) phosphate I 15 Diallyl- 0.5 do. 100 do. 1.2

phenyl phosphate 16 Tri-n-butyl 1.0 p-t-Butyl 100 do. 02

phosphate catechol 17 Tricresyl 0.5 Sodium 50 do. 0.8

phosphate nitrite l8 do. 100 Polymer 6.3

deposits 19* Triphenyl 0.5 do. 100 Clear 0.8

phosphate 20' Tricresyl 015 do. 100 do. 1.0

phosphate Solvent (dimethyl formamide) completely free from water.

Table 2 Polymerization inhibitor Condition Polymer No. lst inhibitors (wt.%) 2nd inhibitors (ppm) after heat content treatment (wt.%)

1 None None Whitens & 12.0

polymer deposits 2 do. Sodium 100 Slightly 1.9

. nitrite whitens 3 Tricresyl 1.0 None Clear 0.9

phosphate 4 do. 0.5 Sodium 100 do. 03

nitrite 5 Tri-n-butyl 1.0 None do. 0.7

phosphate 6 do. 05 p-t-Butyl 200 Lightly 1.1

catechol yellow 7 do. 0.5 Sodium 100 Clear 0.1

I nitrite 8 Triphcnyl 0.5 do. do. 0.2

phosphate 9 Tri(2-chloro- 0.5 do. 50 do. 0.4

ethyl) phosphate Example 3 70 parts of acetonitrile which contained 5 percent by weight of water was mixed with a C hydrocarbon fraction of the composition given in Table 3. With different inhibitors, each of the resulting mixtures was treated with heat for hours in the presence of iron rust in a hermetically sealed vessel at a temperature of C and a gauge pressure of 5 kg/cm The results obtained were as shown in Table 4.

Component vContent(wt.'/n)

Allene 0.002

Table 3-Continued 80 parts of acetonitrile which contained 5 percent by Component Content(wt.%)

Methyl acetylene -0l9 weight of water and 20 parts of butadiene were charged 5:32: into a hermetically sealed vessel. With different inhibil-Butene 22.096 tors, the resulting mixtures were treated with heat for 33-847 70 hours in the presence of iron rust at a temperature n-Butane 2.400 0 2 Trans z butene 4.54] of 120 C and a gauge pressure of 5 kg/cm The results 14690 are given in Table 5.

K83; Experiments were also conducted under the same l,2-Butadiene 0.001 conditions as above except that the solvent acetonitrile was replaced by DMF, NM? or DMAC. In every case, 100.000

the addition of sodium nitrite 100 ppm) alone resulted Table 4 Polymerization inhibitor Condition Polymer No. lst inhibitors (wt.%) 2nd inhibitors (ppm) after heat content treatment (wt.%)

1 None None Polymer 10.6

deposits 2 do. Sodium 100 Slightly 4.2

nitrite whitens 3 do. p-t-Butyl 100 Whitens 7.3

catechol 4 Triphenyl 0.5 None Slightly 1.5

phosphate whitens 5 do. 0.5 p-t-Butyl 100 Clear 1.0

catechol 6 Tricresyl 0.5 Sodium [00 do. 0.2

phosphate nitrite 7 Tri-n-butyl 1.0 None do. 0.7

phosphate 8 Pyridine 1.0 Sodium I00 do. 0.5

nitrite 9 Quinoline 1.0 do. 100 do. 1.2 10 Anthracene l.0 do. 100 do. 0.5

Table 5 Polymerization inhibitor Condition Polymer No. lst inhibitors (wt.%) 2nd inhibitors (ppm) after heat Content treatment (wt.%)

l None None Whitens l0.4

polymer deposits 2 do. Sodium 200 Slightly 3.2

nitrite whitens 3 do. p-t-Butyl 200 do. 4.l

catechol 4 Pyridine 0.5 None do. 2.2 5 do. 0.5 Sodium 200 Clear 07 nitrite 6 do. 10 p-t-Bulyl 200 do. 0.8

catechol 7 a-Picoline 1.0 Sodium l00 do. 0.5

nitrite 8 2-Methyl-5 1.0 do. do. 0.4

ethylpyridine 9 Quinoline 0.5 None Rather 1.7

whitens l0 do. 0.5 Sodium 100 Clear 0.]

nitrite l I do. 1.0 p-t-Butyl 200 do. 0.4

catechol l2 2-Mcthyl 1.0 Sodium I00 do. 0.8

quinoline nitrite I 3 Anthracene 0.5 None Slightly l .5

whitens [4 do. 1.0 Sodium I00 Clear 1.0

nitrite in whitening of the solution in 70 hours, whereas the singular use of. pyridine, quinoline or anthracene (0.5 wt. percent) kept the solutions clear 70 hours later. The transparency of the solutions was maintained for of 7 to l of said C hydrocarbon fraction. The mixture was continuously fed to the tenth stage from the column top, and the column was operated at a reflux ratio of 5.0, a column top temperature of 47 C and a coleven longer periods by the combined use of sodium ni- 5 umn bottom temperature of 100 C. The isoprenetrite (100 ppm) and one of those inhibitors. containing extracting solution was continuously treated The results of EXampl 1 t0 4 giv above d at the next stripping column, and the recovered extracstrate the effect achieved in accordance with the pr tive solvent was directly recycled to the extractive discnt invention for the prevention of polymerization of tillation column, butadiene at elevated tempera u e. The operation was continued for one week, but the extractive solution showed no sign of change and re- Example 5 mamed clear. When the same operation was repeated 70 Parts of acetonm'lle which comamed 5 Pfiment y but without the addition of triphenyl phosphate and soweight of water and 30 parts of isoprene wer mixed dium nitrite to the extractive solvent, the solution with one of the various inhibitors mentioned below, began t be hit d t bid in 10 ho r and gave and the resulting mixtures were treated with heat at a polymer d i li htl orange i color i h 120 C, in the presence of iron rust. The conditions of E l the products were examined, the results being as comxamp e piled in Table 6. Test solutions were prepared under the same condi- Table 6 Polymerization inhibitor Condition after heating No. lst inhibitors (wtF/a) 2nd inhibitors (ppm) 24 hrs. 80 hrs.

1 None None Polymer deposits 2 do. Sodium lOO Slightly Polymer nitrite whitens deposits 3 do. p-t-Butyl 100 Polymer catechol deposits 4 do. Phenyl-B- 100 Polymer naphth'ydeposits lamine 5 Triphenyl 0.5 None Slightly Polymer phosphate whitens deposits 6 do. 0.5 Sodium I00 Clear Clear nitrite 7 do. 0.5 do. do. Slightly whitens 8 Triphenyl 0.5 p-t-Butyl l00 Clear Slightly phosphate catechol Whitens 9 do. 1.0 Phenyl-B- I00 Clear do. naphthylamine l0 Tricresyl 0.5 Sodium 100 do. Clear phosphate nitrite ll Tris(4-t- 0.5 do. 100 do. do.

butylphenyl) phosphate l2 Tri(n)butyl 0.5 do. 100 do. do.

phosphate 7 l3 Tristo-bi- 0.5 do. 100 do. do.

phenyl) phosphate 14 Diallyl- 0.5 do. 100 do. do.

phenyl phosphate Ex mpl 6 tions as described in Example 5 except that N-methyl Into an extractive distillation column having 100- 50 pyrrolidone was employed as the solvent and, with difstage plates, 21 C hydrocarbon fraction containing isoferentinhibitors tabled below, the respective solutions prene was fed, using an extractive solvent prepared by were treated in the presence of iron rust with heat. at adding 0.5 percent by weight of triphenyl phosphate 140 C. The conditions of the solutions were investiand 100 ppm of sodium nitrite to acetonitrile containgated, and the results as given in Table 7 were obing 5 percent by weight of water, ata rate (molar ratio) tained.

Table 7 Polymerization inhibitor Condition after heating No. 15! inhibitors (wt.%) 2nd inhibitors (ppm) 24 hrs. 72 hrs.

1 None None Polymer deposits 2 do. Sodium I00 Slightly Polymer nitrite whitens deposits 3 Triphcnyl 0.5 None Slightly Polymer phosphate whitens deposits 4 do. 0.5 Sodium Clear Clear nitrite 5 Tri( n )butyl 0.5 None Slightly Polymer phosphate whitens deposits do. 05 Sodium 100 Clear Clear nitrite Similar experiments were conducted under the same conditions as above but using dimethyl formamide or dimethyl acetamide in place of N-methyl pyrrolidone hours, while, under the conditions corresponding to those for Exp. Nos. 5, 9 and 13, the extracting solutions were clear.

as the solvent. In each case the use of sodium nitrite E mple 9 (100 ppm) alone led to deposition of polymer in 72 Experiment was conducted under the same condihours, but when sodium nitrite (100 ppm) and tri-ntions as described in Example 6 except that 0.5 percent butyl phosphate (0.5 wt. percent) were added, the test by weight of pyridine and 100 ppm of sodium nitrite solution remained clear 72 hours later. were used as the inhibitors.

The operation was continued for 5 days, but the ex- Example 8 tracting solution showed no sign of'change and remained clear. When pyridine was replaced by quinoline 7() parts f it il hi h Contained percent b or anthracene, the results were similar to those attained weight of water and 30 parts of isoprene were mixed Wlth Py and, with the addition of various inhibitors tabled be- In the absence of py quinoline, n ene r low, the respective mixtures were treated in the pressodium nitrite, the extracting solution began to become once of iron rust at 120 C, and the conditions of the White and turbid In 10 u s and d posited a lightly products were investigated. The results are given in Orange P y hours- Table 8. Example 10 20 Table 8 Polymerization inhibitor Condition after heating No. lst inhibitors (wtF/r.) 2nd inhibitors (ppm) 24 hrs. 48 hrs.

1 None None Polymer deposits 2 do. Sodium 200 Slightly Polymer nitrite whitens deposits 3 do. p-t-Butyl 200 Polymer catechol deposits 4 Pyridine 0.5 None Rather Polymer turbid deposits 5 do. 0.5 Sodium 200 Clear Clear nitrite v 6 do. 1.0 do. 100 do. do. 7 do. 1.0 p-t-Butyl 200 Slightly Rather catechol whitens turbid 8 Ouinoline 0.5 None Rather Polymer turbid deposits 9 do. 0.5 Sodium 200 Clear Clear nitrite Y 10 do. 1.0 do. 100 do. do. 1 1 do. 1.0 p-t-Butyl 200 Slightly Rather catechol whitens turbid l2 Anthracene 0.5 None Rather Polymer turbid deposits 13 do. 0.5 Sodium 200 Clear Clear nitrite 14 do. 1.0 do. 100 do. do. 15 Anthracene 1.0 p-t-Butyl 200 Slightly Rather catechol whitens turbid Experiments were conducted under the same condi- Under the same conditions as used in Example 8, test tions for Exp. Nos. 4, 5, 8, 9, 12 and 13 in Table 8 exsolutions were prepared with the addition of various incept that the solvent acetonitrile was replaced by N- hibitors mentioned in Table 9, and the mixtures were methyl pyrrolidone or dimethyl formamide. Then, treated in the presence of iron rust at 120 C, and then under the conditions corresponding to those for Exp. Nos. 4, 8 and 12, slight turbidity was observed the conditions of the products were examined. The results obtained were as shown in Table 9.

Table 9 Polymerization inhibitor Condition after heating No. 1st inhibitors (wt.%) 2nd inhibitors (ppm) 24 hrs. 48 hrs.

1 Z-Methyl 0.5 None Rather Polymer pyridine turbid deposits 2 do. 0.5 Sodium 200 Clear Clear nitrite 3 do. 1.0 do. do. do. 4 do. 1.0 p-t-Butyl 200 Slightly Rather catechol whitens turbid 5 2.3-Dimethyl 0.5 None Rather Polymer pyridine turbid deposits 6 do. 05 Sodium 200 Clear Clear nitrite 7 do. 1.0 do. 100 do. do. 8 do. 1.0 p-t-Butyl 200 Slightly Rather catechol whitens turbid 9 2-Methyl-4- 0.5 None Rather Polymer ethyl pyridine V turbid deposits Table 9 Continued Polymerization inhihitor Condition after heating No. Is! inhibitors (wtf/r) 2nd inhibitors (ppm) 24 hrs. 48 hrs.

10 do. 0.5 Sodium 200 Clear Clear nitrite l I do. 1.0 do. 100 do. do. 12 do. 1.0 p-t-Butyl 200 Slightly Rather catcchol whitens turbid l3 2-Methyl 0.5 None Rather Polymer quinolinc turbid deposits 14 do. 05 Sodium 200 Clear Clear nitrite 15 do. 1.0 do. 100 do. do. 16 do. 1.0 p-t-Butyl 200 Slightly Rather catechol whitens turbid l7 4-Ethyl 0.5 None Rather Polymer quinoline turbid deposits 18 do. 0.5 Sodium 200 Clear Clear nitrite 19 do. 1.0 do. [00 do. do. 20 do. 1.0 p-t-Butyl 200 Slightly Rather catechol whitens turbid We claim: (wherein R R and R are phenyl group or nuclear 1. A process for preventing the polymerization of conjugated dienes in solvents at high temperature characterized by the addition of at least one compound selected from the group consisting of organic phosphoric acid esters of the general formula 3. A process for preventing the polymerization of isoprene in a solvent at elevated temperature characterized by the addition of at least one compound selected from the group consisting of organic phosphoric acid esters of the general formula substituted derivatives thereof whose substituents being alkyl groups, phenyl group or halogen atoms; alkyl groups; halogen substituted alkyl groups, or allyl group), to the solvent containing isoprene as inhibitor.

4. A process for preventing the polymerization of conjugated dienes as defined in claim 1 wherein the organic phosphoric acid esters are triphenyl phosphate and nuclear substituted derivatives thereof wherein the substituents are alkyl groups, phenyl group or halogen atoms, trialkyl phosphates with or without substituted halogen atom, allylbiphenyl phosphate and diallylphenyl phosphate.

5. A processfor preventing the polymerization of conjugated dienes as defined in claim 4 wherein the triphenyl phosphates and nuclear substituted derivatives thereof are triphenyl phosphate, tri(o-cresyl) phosphate, tri(rn-cresyl) phosphate, tri(p-cresyl) phosphate, trixylenyl phosphate, tris(4-t-butylphenyl) phosphate, tris(o-biphenylyl) phosphate.

6. A process for preventing the polymerization of conjugated dienes as defined in claim 4 wherein the trialkyl phosphates and halogen substituted derivatives thereof are trimethyl phosphate, triethyl phosphate, tri(n)propyl phosphate, tri(i)propyl phosphate, tri(n- )butyl phosphate, tri(sec)butyl phosphate, tri(n)amyl phosphate, trihexyl phosphate, triheptyl phosphate, trioctyl phosphate and other organic phosphoric acid esters wherein the alkyl groups have from 1 to 8 carbon atoms; and tri(2-chloroethyl) phosphate, tri(2- bromoethyl) phosphate, tri(3-chloropropyl) phosphate, tri(3-bromopropyl) phosphate, tri(3- iodopropyl) phosphate, tri(2,3-dichloropropyl) phosphate, tri(2,3-dibromopropyl) phosphate, tri(2,3- diiodopropyl) phosphate, tri(4-chlorobutyl) phosphate, tri(4-bromobutyl) phosphate, tri(4-iodobutyl) phosphate.

7. A process for preventing the polymerization of conjugated dienes as defined in claim 4 wherein the organic phosphoric acid esters which contain phenyl and allyl groups are diallylphenyl phosphate and allylbiphextylphqsrh ts 8. The process of claim 1 wherein a known polymerization inhibitor or antio tidant for unsaturated cornwherein R R and R are phenyl group or nuclear substituted derivatives thereof whose substituents being alkyl groups, phenyl group or halogen atoms; alkyl groups; halogen substituted alkyl groups, or allyl group, to the solvent containing the conjugated diene as a first inhibitor, and wherein a known polymerization inhibitor or antioxidant for unsaturated compounds selected y from the group consistingof sodium nitrite, potassium nitrite, sodium sulfide, a phenolic compound and an aromatic amine compound is used as a second polymeriz ation inhibitor.

11. The process of claim 10 wherein the second poly merization inhibitor is sodium nitrite.

PHIN I hH'S IHIM L UNITED STATES PATENT OFFICE CERTEFECATE OF CORRECTION Patent No. 3 80 0 O02 Dated March 26, 1974 inventor) Tatsusuke Chikatsu et a1 It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In the heading of the patent, insert --[30] Foreign Application Priority Data March 20, 1970 Japan .45-23740 July 9, 1970 Japan ..4560034 Oct. 5, 1970 Japan ..4587366 Signed and sealed this 12th day of November 1974.

(SEAL) Attest:

MCCOY M. GIBSON JR. 0. MARSHALL DANN Attesting Officer Commissioner of Patents FORM P0405) (10-59) USCOMM-DC ooa'lc-poo Q LLS. GOVERNMENT PRINTING OFFICE IQ, 3-33, 

2. A process for preventing the polymerization of butadiene in a solvent at elevated temperature characterized by the addition of at least one compound selected from the group consisting of organic phosphoric acid esters of the general formula
 3. A process for preventing the polymerization of isoprene in a solvent at elevated temperature characterized by the addition of at least one compound selected from the group consisting of organic phosphoric acid esters of the general formula
 4. A process for preventing the polymerization of conjugated dienes as defined in claim 1 wherein the organic phosphoric acid esters are triphenyl phosphate and nuclear substituted derivatives thereof wherein the substituents are alkyl groups, phenyl group or halogen atoms, trialkyl phosphates with or without substituted halogen atom, allylbiphenyl phosphate and diallylphenyl phosphate.
 5. A process for preventing the polymerization of conjugated dienes as defined in claim 4 wherein the triphenyl phosphates and nuclear substituted derivatives thereof are triphenyl phosphate, tri(o-cresyl) phosphate, tri(m-cresyl) phosphate, tri(p-cresyl) phosphate, trixylenyl phosphate, tris(4-t-butylphenyl) phosphate, tris(o-biphenylyl) phosphate.
 6. A process for preventing the polymerization of conjugated dienes as defined in claim 4 wherein the trialkyl phosphates and halogen substituted derivatives thereof are trimethyl phosphate, triethyl phosphate, tri(n)propyl phosphate, tri(i)propyl phosphate, tri(n)butyl phosphate, tri(sec)butyl phosphate, tri(n)amyl phosphate, trihexyl phosphate, triheptyl phosphate, trioctyl phosphate and other organic phosphoric acid esters wherein the alkyl groups have from 1 to 8 carbon atoms; and tri(2-chloroethyl) phosphate, tri(2-bromoethyl) phosphate, tri(3-chloropropyl) phosphate, tri(3-bromopropyl) phosphate, tri(3-iodopropyl) phosphate, tri(2,3-dichloropropyl) phosphate, tri(2, 3-dibromopropyl) phosphate, tri(2,3-diiodopropyl) phosphate, tri(4-chlorobutyl) phosphate, tri(4-bromobutyl) phosphate, tri(4-iodobutyl) phosphate.
 7. A process for preventing the polymerization of conjugated dienes as defined in claim 4 wherein the organic phosphoric acid esters which contain phenyl and allyl groups are diallylphenyl phosphate and allylbiphenyl phosphate.
 8. The process of claim 1 wherein a known polymerization inhibitor or antioxidant for unsaturated compounds selected from the group consisting of sodium nitrite, potassium nitrite, sodium sulfide, a phenolic compound and an aromatic amine compound is used as a second polymerization inhibitor.
 9. A process for preventing the polymerization of conjugated dienes as defined in claim 8 wherein the second polymerization inhibitor is sodium nitrite.
 10. A process for preventing the polymerization of conjugated dienes in solvents at high temperature characterized by the addition of at least one compound selected from the group consisting of organic phosphoric acid esters of the general formula
 11. The process of claim 10 wherein the second polymerization inhibitor is sodium nitrite. 